Stepper Motors. Any Experts?

I've been learning and trying to reverse-engineer the logic, nature and anatomy of a stepper motor.

These motors come with certain specs as far as Vmax, A/phase and so forth. I have learned that a 1.8degree motor is 360/1.8 = 200 steps in the motor.

when trying to calculate desired RPM you use PPS (Pulse Per Second). in this case if we choose a desired 500RPM for the motor to output... the math would show:

(500Rpm / 60sec-min) = 8.33Rps.
Then
(200steps-in-motor-per-rev X (8.33Rps)) = 1,666 PPS.

My question is: If I want 500Rpm out of this motor....and I need 1,666 pulses per second to achieve 500Rpm, how is PPS a function of Voltage, Amperage and resistance? What would be the draw of the motor in and V and A at 500Rpm and 1,666PPS?

 

I understand better now. And oh yes I remember the old floppies! The first apples came out when I was in gradeschool. The 5.25-inch versions. I can remember those PC's loading for decades and the disk drive sounding like a meat grinder just to play "The Oregon Trail" game.

Given that PPS is basically a number corresponding to number of steps, is there another way to calculate rpm given the specifications shown here? (http://www.applied-motion.com/products/stepper-motors/ht17-075) -spec tab at bottom left.

Listed is the V/phase and A/phase and R. Would I assume that if this motor has 200steps and I met the PPS equivalent to the RPM of 200 steps that the motor would only draw the listed voltage shown in the data?

 

QUOTE]
Do you understand that the stepper motor is driven with a sequence of pulses alternating among the different phases?

Bob[/QUOTE]

True, I understand, but if there are 200 steps in 1 revolution, and we are operating the motor at 1 full step interval continually to provide continuous motion of the shaft at the motors rated voltage, what would be the rpm? I am basically trying to make the distinction between the number of steps in a the motor, and how the number of steps in the motor is related to continuous motion @ the given voltage and amperage rating with no load thus giving me its maximum rpm rating. How is one to know this?

 

Basically what Im trying to figure out is how RPMout is a function of Pulse, Voltage, or current In. If I could calculate this somehow then I would know how much RPMin I need to get V and I out for something like this:



The main reason I need to know RPM-out/RPM-in @ a given voltage via the motor's specs. is because I need to know what pulleys and gears I need for the correct ratio. Unfortunately these motor mfg's dont list rpm, only V, I, R, Mh, per phase. Thus I have been trying to reverse engineer the nature of this and figure out how pulses and frequency relate to input voltage or amperage so that I dont have to buy gears or pulleys 5 times to get the right speed. I think I am just going to buy various motors and experiment.

 

Power in = Torque out as Torque in = power out. Is that helpful? Or do you need to watch this:



If I know what RPM the motor makes at a given voltage, then I know what input rpm I need to get a (near) output voltage +-

 

True and I have calculated all this, I was just trying to estimate my gear ratios by finding a way to calculate the RPM and Voltage relation @ 0.95A draw. I talked with one of the Mfg's of a stepper and now I know which motor I need. I think the easiest way im gonna figure this out before ordering gears is to hook the motor up, rectify it, regulate it and load it to what I need...and then read the Rpm at that moment. This way I can select an appropriate gear before attaching it to my engine.

Originally I was just trying to reverse the math to figure out a ballpark figure of RPM out at a given voltage, so that I might estimate what rpm would provide said voltage.

 

True, I will just have to adjust the gear ratio accordingly to match the rpm I need.

The reason I am using a stepper is because steppers generate much more voltage at low rpm compared to normal DC motors. I have experimented with other DC motors, one having a (lower than normal) Kv value of 236Kv, so to get 12V out of it I need to turn it at 2,832 Rpm. That motor has a greater amperage rating than a stepper, but takes more input.

From what i've researched, I should be able to get the same or more voltage by turning a stepper motor at 200 to 300 rpm and wiring the 2 phase output across a voltage doubler circuit.

The project objective is to obtain enough DC power after rectification and regulation, to meet the 5V 950Ma rating of standard USB power for charging USB devices. The other reason for trying to use a stepper is the scale. My power plant is a 1/2" bore micro steam engine with a maximum rpm of around 500. I want to be able to obtain unconventional dc power from fire and water to charge devices and batteries. The best I can figure the engine is probably capable of 40 watts output. I want to use a stepper for the lower rpm so I dont lose much torque due to increasing the speed of the output gear.

So in the end, I basically started this thread to see if I there was a way to calculate Rpm through the math and given values of the motor. I know it varies with voltage and at this point I think my best bet is to attach the stepper to another DC motor on a PoT and slowly increase speed until I read the value I need across the rectified stepper output circuit.

 

Thanks for the linkage and comments guys. I am pretty sure this is going to work, I will just have to continue testing. I've become obsessed with the project and with winter coming on I should have a bit of time to iron it out.....Today I started thinking about the exhaust of the steam engine and the concept of a coiled exhaust system coupled to the hot side of a thermoelectric generator plate.

This way I can harness the heat lost as the steam condenses back to liquid and convert it to extra energy! the question is... how do I incorporate a lower thermoelectric current back into the output power of the alternator? It would be a lower voltage than the alternator but would it be wired in series or parallel? The quest continues. seems like I keep adding more and more to it, but the end result should be pretty cool. I am hoping to fit the entire unit into a .50 caliber steel ammo box. I will post a good video up to youtube when I complete this.

Hopefully it will charge the iPhone and other devices with no problem. I am going to modify the resistance on the signal wires of the USB out so that the iPhone will only only draw 500mA instead of the 1A the proprietary apple charger pulls.